African crested rats deter predators by borrowing poison bark

Scientists have found the first example of a mammal that uses poison from …

Mammals have all sorts of interesting and novel defense tactics: sharp quills, stinky spray, and clever camouflage, among others. Some mammals even produce poison to deter predators looking for a meal. Now, scientists have identified the first mammal that uses poison—but gets it from another species. Last week’s issue of Proc B reports that the African crested rat chews bark from a particular plant, then smears the slimy paste onto specialized hairs that can deliver the toxin to a hungry predator’s mouth.

The African crested rat is a large gray rodent that lives in (wait for it...) Africa. It resembles a porcupine at first glance. In general, these rats are pretty sluggish and inconspicuous but, when threatened, they fluff up a row of hairs along their backs, exposing a bright black and white pattern. They also turn away from the predator, pointing their hairy mohawks and brightly patterned flanks toward the threat. Until recently, scientists weren’t sure why such a slow-moving animal would seemingly invite an attack with this bold display.

But an in-depth study of the African crested rat shows that this display, as well as the morphology of the rat, is a highly evolved method to deter predators. First, the rats chew up bark from the a particular type of East African tree,called Acokanthera schimperi. Once the bark softens, the rats smear the paste on the specialized hairs along its back. If the rat drops any of the chewed bark, he carefully picks it up and smears these pieces on as well. The rats perform this behavior regularly; a wild-caught rat in captivity prepped himself with poison three times over five days.

Using an scanning electron microscope, the scientists found that these particular hairs are structured to store and deliver poison. The toxin in the bark is absorbed into the hair through capillary action and stored inside the hair shaft. Once this process is complete, touching the hairs will deliver a large dose of strong toxin.

The toxin found in the bark of in A. schimperi is called ouabain, and has long been used in offensive weaponry: poison-tipped arrows made by humans. Ouabain increases the force of muscle contractions in the heart, leading to a loss of coordination, collapse, and sometimes death.

Here is where the rat's strange defensive behavior comes in: to maximize the chance of a predator's delicate mouth coming into contact with the toxin, the rat turns its back and fluffs up these particular poison-holding hairs. If the predator hasn't come into contact with the rat before, it will probably bite, getting a large dose of toxin delivered directly into its mouth. If it survives the ordeal, the next time the predator sees the memorable black and white pattern, it will probably think twice about taking the bait.

There are still many unanswered questions about this defense tactic, including one that should be obvious: why don't the rats poison themselves while chewing the bark? This is the first known example of a non-human mammal acquiring a poisonous compound from another species and using it for its own defense. The entire suite of adaptations, from bark-chewing to specialized hairs to defensive behavior, is an elegant solution to nearly every animal's task of defending itself against predators.

Kate Shaw Yoshida
Kate is a science writer for Ars Technica. She recently earned a dual Ph.D. in Zoology and Ecology, Evolutionary Biology and Behavior from Michigan State University, studying the social behavior of wild spotted hyenas. Emailkate.shaw@arstechnica.com//Twitter@KateYoshida

Scientists have found the first example of a mammal that uses poison from another species as its own defense strategy.

So humans aren't mammals anymore? Humans have been doing this for thousands of years.

Just go with it.

Human adaptive behavior is predominately cognitive. The rat's defense is evolved, it probably doesn't even comprehend why it does what it does, it's just compelled to do it by instinct.

Cognitive adaptation works so much faster then evolution that it's really not news to say humans can do something too. The Native Americans didn't need to evolve animal husbandry and metallurgy to make use of the guns and horses the French traded to them.

Scientists have found the first example of a mammal that uses poison from another species as its own defense strategy.

So humans aren't mammals anymore? Humans have been doing this for thousands of years.

Just go with it.

Human adaptive behavior is predominately cognitive. The rat's defense is evolved, it probably doesn't even comprehend why it does what it does, it's just compelled to do it by instinct.

Cognitive adaptation works so much faster then evolution that it's really not news to say humans can do something too. The Native Americans didn't need to evolve animal husbandry and metallurgy to make use of the guns and horses the French traded to them.

I hear Leonard Nimoy's voice when I read that: "*ding* You have evolved Animal Husbandry."

@Mandor: thanks for the video link. for some reason I had a mental picture of the rat trying to smear it all along its back, not just at the base or lower back. My dog chews himself there all the time. Now I can see how a rat would do it, too.

They also turn away from the predator, pointing their hairy mohawks and brightly patterned flanks toward the threat. Until recently, scientists weren’t sure why such a slow-moving animal would seemingly invite an attack with this bold display.

How do the rats smear the poison on their backs? Do they just turn around and spit it out, or are their front paws able to reach back there...?

Yeah rats are extremely flexible and can reach just about any part of their body with their with both their paws and mouth (the exception being the top of their head which they clean with their hands). They can also slip out of any bandage you put them in, which makes it quite difficult to keep them from chewing on sutures if they decide they want to :)

I'm reminded of a scene from Life; in the American west, squirrels will chew up shed rattlesnake skins and smear the paste into their tails. Since rattlesnakes hunt largely by scent, the squirrel can wave its tail that now smells like rattlesnake to convince a snake that there is no prey, but rather just another snake.

I do something similar... I drink pots of coffee every day so if blood sucking arthropods bite me their hearts burst within seconds.

Wow, we're kindred spirits then! I just happen to drink so much Cola that a vampire would fall in sugar-induced coma within seconds. Plenty useful. Not to mention that my blood is also pretty useful when baking stuff and you run out of regular sugar!

Note, when they this is the first know "poisonous" mammal, they are using the technical, uncommon meaning of the word. Platypus (a mammal, if a weird one) have long been known to have "venomous" spurs. It the technical sense, "venomous" is an animal that actively injects you with a toxin, while "poisonous" animals have toxins in or on the body.

Note, when they this is the first know "poisonous" mammal, they are using the technical, uncommon meaning of the word. Platypus (a mammal, if a weird one) have long been known to have "venomous" spurs. It the technical sense, "venomous" is an animal that actively injects you with a toxin, while "poisonous" animals have toxins in or on the body.

They're not actually saying that the mammal itself is "poisonous," they're saying that it's utilizing poison in its environment and can do this through some evolutionary adaptations. The platypus makes it's own venom, so it truly is "venomous."

Smart rodent, but I wish Ars writers would proof-read themselves before publishing an article, not just rely on a spellchecker:

"from the a particular type of East African tree""Using an scanning electron microscope""The toxin found in the bark of in A. schimperi"

And maybe do some research as well:"The African crested rat is a large gray rodent that lives in (wait for it...) Africa."There is no such animal. Its name is the maned rat or crested rat. It is as bad as thinking there is a city called "The European City of Paris" and saying that it is located in Europe.And as imprecise, since readers should know the crested rat lives more precisely in East Africa, where this poisonous tree grows (which you mention.)

"touching the hairs will deliver a large dose of strong toxin"Actually touching the hairs will do nothing since the poison is inside the hair. You need to be prickled or rather stung to transfer the poison through the skin tissues.I touch hedgehogs (perv!) several times a year to clean them from ticks, never been stung once.

I definitely don't think they're the first to exhibit that sort of behavior. I instantly remembered something from my childhood (I watched WAAAAY too much Discovery Channel), and had to do some research as I didn't remember the name of the ants.... Southern Wood Ants.

They shoot acid at attackers. There are some birds that have an immunity to it, and will purposely harass a colony so they are sprayed by the ants, which kills and prevents infestation by parasites.

"Indeed, some birds deliberately annoy the ants, and then daub the formic acid on themselves as a pesticide that guards against tics, mites and other unpleasant, plumage occupants – the process is known as anting."~ http://www.newforestexplorersguide.co.u ... tpage.html

I definitely don't think they're the first to exhibit that sort of behavior. I instantly remembered something from my childhood (I watched WAAAAY too much Discovery Channel), and had to do some research as I didn't remember the name of the ants.... Southern Wood Ants.

They shoot acid at attackers. There are some birds that have an immunity to it, and will purposely harass a colony so they are sprayed by the ants, which kills and prevents infestation by parasites.

"Indeed, some birds deliberately annoy the ants, and then daub the formic acid on themselves as a pesticide that guards against tics, mites and other unpleasant, plumage occupants – the process is known as anting."~ http://www.newforestexplorersguide.co.u ... tpage.html